1. Field of the Invention
The present disclosure relates to a liquid crystal display (LCD) device and a method for fabricating the same, and more particularly, to an LCD device capable of enhancing an aperture ratio and a transmittance ratio, and a method for fabricating the same.
2. Background of the Invention
Recently, as a demand for portable information media increases with high concerns about information display, a light, thin and small flat panel display (FPD) device replacing the conventional display device, a cathode ray tube (CRT) is being spotlighted. Research on the FPD and commercialization thereof are being actively done. Among such FPD devices, a liquid crystal display (LCD) device which displays an image using optical anisotropy of a liquid crystal, is widely applied to a notebook computer, a desk top monitor, etc. owing to its superior resolution, color display, picture quality, etc.
The LCD device largely consists of a color filter substrate, an array substrate, and a liquid crystal layer formed between the color filter substrate and the array substrate.
A representative driving method for the LCD device, an active matrix (AM) method is a method for driving a liquid crystal of a pixel region by using an amorphous silicon thin film transistor (a-Si TFT) as a switching device.
Hereinafter, a structure of the conventional LCD device will be explained in more details with reference to FIG. 1.
FIG. 1 is an exploded perspective view schematically illustrating a structure of a liquid crystal display (LCD) device in accordance with the related art.
As shown, the LCD device largely consists of a color filter substrate 5, an array substrate 10, and an LC layer 30 formed between the color filter substrate 5 and the array substrate 10.
The color filter substrate 5 includes a color filter (C) consisting of a plurality of sub color filters 7 for implementing colors of red, green and blue (RGB); a black matrix 6 for separating the sub color filters 7 from each other, and blocking light which penetrates through the LC layer 30; and a transparent common electrode 8 for applying a voltage to the LC layer 30.
The array substrate 10 includes a plurality of gate lines 16 and data lines 17 which define a plurality of pixel regions (P) by crossing each other; thin film transistors (TFT) formed at intersections between the gate lines 16 and the data lines 17; and pixel electrodes 18 formed on the pixel regions (P).
The color filter substrate 5 and the array substrate 10 are disposed to face each other, and are attached to each other by a sealant (not shown) formed at the outer periphery of an image display region, thereby implementing an LCD panel. The color filter substrate 5 and the array substrate 10 are attached to each other by a bonding key (not shown) formed at the color filter substrate 5 or the array substrate 10.
As a general driving method for the LCD device, there is a twisted nematic (TN) method for driving nematic phase LC molecules in a direction perpendicular to a substrate. However, the TN method has a disadvantage that a viewing angle is narrow (e.g., about 90°), which results from refractive anisotropy of LC molecules. More specifically, the reason why the viewing angle is narrow is because LC molecules aligned in a horizontal direction with respect to the substrate are aligned in a direction perpendicular to the substrate, when a voltage is applied to an LCD panel.
In order to solve such problem, there has been proposed a Fringe FieldIn Switching (FFS) mode LCD device for enhancing a viewing angle to 170° or more, by driving LC molecules in a horizontal direction with respect to the substrate. This will be explained in more details.
FIG. 2 is a planar view illustrating a structure of an FFS mode LCD device in accordance with the related art.
As shown in FIG. 2, in the conventional FFS mode LCD device 10, a plurality of gate lines 16 and data lines 17 are formed on a transparent substrate (array substrate) in horizontal and vertical directions (i.e., they cross each other), thus to define a plurality of pixel regions. A thin film transistor (TFT) 20, a switching device is formed at each intersection between the gate line 16 and the data line 17. Generally, the gate line 16 is formed in ‘N’ in number, and the data line 17 is formed in ‘M’ in number, thereby forming ‘N×M’ pixel regions. However, for convenience, a single pixel region is illustrated in the drawings.
The TFT 20 includes a gate electrode 21 connected to the gate line 16, a source electrode 22 connected to the data line 17, and a drain electrode 23 connected to a pixel electrode 18.
Also, the TFT 20 includes gate insulation layers (not shown) for insulating the gate electrode 21 and the source/drain electrodes 22 and 23 from each other, and a semiconductor layer 25 (i.e., active pattern) for forming a conductive channel between the source electrode 22 and the drain electrode 23 by a gate voltage supplied to the gate electrode 21.
In the pixel region, box-shaped common electrode 8 and pixel electrode 18 are formed. The common electrode 8 includes a plurality of slits 8s therein so as to generate a fringe field together with the pixel electrode 18.
The common electrode 8 is electrically connected to a common line 81 disposed in parallel to the gate line 16, through a contact hole 40 of an insulation layer (not shown).
In the FFS mode LCD device, as a scan signal is applied to the gate electrode 21 of the TFT 20 through the gate line 16, the semiconductor layer 25 of the TFT 20 is activated, thereby forming a conductive channel. At the same time, an image signal input to the data line 17 is input to the pixel electrode 18 via the source electrode 22 and the drain electrode 23 of the TFT 20. As a result, an electric field is formed between the common electrode 8 and the pixel electrode 18, so that an image is implemented.
However, the conventional FFS mode LCD device has the following problems.
As shown in FIG. 2, the TFT 20 is formed at each pixel region, and the common electrode 8 and the pixel electrode 18 are not formed at a region where the TFT 20 is formed. The region where the TFT 20, the gate line 16 and the data line 17 are formed, is a non-display region where an image is not implemented. Light may leak to the non-display regions, and thus picture quality may be lowered. Therefore, the non-display regions should be blocked by a black matrix 42 formed of black resin, etc., so that light transmittance can be prevented.
The TFT 20 occupies most of a lower region of a pixel. That is, a region (A) disposed at an image display region of a pixel adjacent to the TFT 20 of a corresponding pixel has an area smaller than that of the TFT 20. The common electrode 8 and the pixel electrode 18 are formed at the region A. However, the region A is not an image display region, when considering a processing margin at the time of forming a TFT of an LCD device, or an attachment margin between a TFT array substrate and a color filter substrate. Therefore, the black matrix 42 is entirely formed on the lower region of the pixel so as to cover the region A.
In the conventional LCD device, the lower region of the pixel where the TFT 20 is formed is an non-display region where light transmittance is prevented. This may cause an aperture ratio and a transmittance ratio of the LCD device to be lowered.